Bone anchoring device and bone stabilization device including the same

ABSTRACT

A bone anchoring device, includes a receiving part for receiving a rod-shaped implant element, the receiving part having a first bore coaxial with a longitudinal axis and extending from a first end of the receiving part, and a recess extending from the first end to accomplish insertion of the rod-shaped implant element. The device further includes a bone screw having a threaded section for insertion into the bone and being fixed at or positionable at a second end of the receiving part and a fixation element provided to the first bore to fixate a rigid section of the rod-shaped implant element. The rigid section of the rod-shaped implant element has a first width, and the recess of the receiving part has a second width. The second width is larger than the first width, such that the recess may accommodate a stepped portion of the rod-shaped implant element that has an increased thickness.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.12/238,347, filed Sep. 25, 2008, now U.S. Pat. No. 8,394,126, issued onMar. 12, 2013, which claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/979,193, filed Oct. 11, 2007, the contents ofwhich are hereby incorporated by reference in its entirety, and claimspriority from European Patent Application EP 07019942.7, filed Oct. 11,2007, the entire disclosures of which are incorporated herein byreference.

BACKGROUND

The present application relates to a bone anchoring device and a bonestabilization device.

A bone anchoring device typically includes a receiving part forreceiving a rod-shaped implant element, a bone screw having a threadsection for insertion into a vertebral body of a spinal column, and afixation element for fixating the rod-shaped implant element within thereceiving part.

The rod-shaped implant element received by the above bone anchoringdevice may typically be connected to a further bone anchoring devicethat is similarly anchored in an adjacent vertebral bone in order tostabilize affected parts of the vertebral column.

One example of a bone stabilization device including two of the abovebone anchoring devices and a rod-shaped implant element (in thefollowing also referred to as a “rod element”) is described in documentEP 1757243 A1, by the same applicant. Therein, a rod element isdisclosed which is composed of a rigid section, a flexible section, abore formed within the rod element and a core. The core is providedinside the bore and extends through parts of the rigid sections andthrough the flexible section.

The flexible section may be made of a cylindrical pipe, into which ahelical opening extending from the inner bore to the outer surface isformed. The resulting flexible section is characterized by its axialcompression or expansion stiffness. The stiffness is achieved by acombination of pitch, web thickness and using biocompatible material'selasticity.

The core may freely slide inside the bore in axial direction at leastwith regard to one of its ends. Thereby, the free end is guided in arigid section adjacent to the flexible section. The bending stiffness ofthe core is bigger than of the flexible section itself. Hence, thebending characteristics of the rod element are determined mainly by thecore.

According to EP 1757243 A1, due to the presence of a bore whichaccommodates the core, the diameter or width of the rod elementincreases as compared with a common rod element, in which flexiblecomponents are not utilized.

The one specific bone anchoring device designed to receive the endsection of the rod element is provided with small openings instead ofthe recesses. The end section of the rod element can be introducedthrough the openings, whose widths correspond to the reduced width ofthe end section.

Based on the above, there is a need for an improved bone anchoringdevice, which provides an enhanced flexibility with regard to astabilization device including a rod element, and to provide a reliablebone anchoring device which facilitates the implantation ofstabilization devices in cases where distance requirements with regardto two adjacently placed bone anchoring devices become very strong,i.e., cases where the mutual distances of those devices are considerablyreduced.

SUMMARY

According to one aspect, there is provided a bone anchoring devicehaving a receiving part for insertion of a rod-shaped implant element(in the following also referred to as a “rod element”). The recessextends from a first (upper) end of the receiving part towards a bottomsection. At least in its bottom section, the recess attains a width(first width), which is larger than that of a section of the rod element(second width), which is to be fixated by the fixation element.

Hence, there is no play and the reliability of the anchoring device andthe fixation of the rod element is increased by a quasi form-fitconnection. This kind of connection may even improve the behaviour ofthe device with regard to strong forces exerted on the rod element inaxial direction, which might else act to slip the rod through thereceiving part.

When using such a stepped rod element in the recess, the minimumdistance between the bone anchoring device is reduced. As will bedescribed in the embodiments below, the stepped portion may represent aflexible section of the rod element. Thereby, in order to maintaindesired properties like bending, compression, expansion, torsionstiffness, etc., in combination with fatigue strength, a minimum lengthof the flexible section is needed.

In case the mutual distance of two adjacent bone anchoring devices (morespecifically: of two opposing surfaces of adjacent receiving parts)would decrease below that minimum length, a bone anchoring device asproposed herein may be utilized to increase the usable length for theflexible section by virtue of the recess being enlarged in width toreceive portions of the flexible section.

According to another aspect related to a polyaxial anchoring device, apressure element is provided which serves to transmit pressure exertedby the fixation element to a head section of the bone screw. The headsection can be positioned in a bore at the bottom end of the receivingpart. The pressure element has a cylindrical recess adapted to receivethe rigid section of the rod element. The cylindrical recess has thefirst smaller width corresponding to the width of the rod element. Thepressure element according to this aspect is further provided with astop face. The stop face is designed to engage with an end face of thestepped portion of the rod element.

In an alternative aspect related to a monoaxial anchoring device, acylindrical recess is provided at a bottom portion of a bore of thereceiving part and is adapted to receive the rigid section of the rodelement. Similar to the previous aspect, the cylindrical recess has thefirst smaller width corresponding to the width of the rod element.Further a stop face is oriented towards the recess having the largerwidth.

In one specific embodiment, the stop face is formed as a plane surfacerecessed from a generally cylindrically shaped surface of the pressureelement.

According to this aspect, the pressure element may provide a form-fitconnection with regard to the stepped rod element as well as with regardto a spherically or cylindrically shaped head section of the bone screw.Due to the recessed stop face, the stepped portion may reach into theinner space of the first bore formed in the receiving part, such thateven more length can be reserved for accommodating the flexible sectionof the rod element, i.e., the mutual distance of the anchoring devicescan be further reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be better understood with reference to specificembodiments of the disclosure when taken in conjunction with theaccompanying drawings. Therein,

FIG. 1 shows an illustration of the spinal column;

FIG. 2 shows an exploded view of a bone anchoring device according to anembodiment of the disclosure;

FIG. 3 shows the bone anchoring device of FIG. 2, but in an assembledstate;

FIG. 4 shows in an enlarged perspective view a receiving part of thedevice according to FIG. 2;

FIG. 5 shows a top view of the receiving part of FIG. 4;

FIG. 6 shows a cross-sectional view of the receiving part according toFIG. 4;

FIG. 7 shows a side view of the receiving part according to FIG. 4;

FIG. 8 shows a front view of the receiving part according to FIG. 4;

FIG. 9 shows in an enlarged perspective view a pressure element of thedevice according to FIG. 2;

FIG. 10 shows a front view of the pressure element according to FIG. 9;

FIG. 11 shows a side view of the pressure element according to FIG. 9;

FIG. 12 shows a cross sectional profile of a bone stabilization deviceincluding the bone anchoring device of FIG. 2;

FIG. 13 shows an enlarged portion of FIG. 12;

FIG. 14 shows a first step of assembling the bone stabilization deviceof FIG. 12 in a side view;

FIG. 15 shows a second (final) step of assembly of the bonestabilization device of FIG. 14;

FIG. 16 shows a first step of assembling the bone stabilization deviceof FIG. 12 in a perspective view;

FIG. 17 shows a second (final) step of assembly of the bonestabilization device of FIG. 14 in a perspective view,

FIG. 18 shows an exploded view of a bone anchoring device according to asecond embodiment of the disclosure;

FIG. 19 shows a perspective view of the bone anchoring device of FIG.18, with the fixation screw being screwed-in;

FIG. 20 shows in an enlarged front view a receiving part of the deviceaccording to FIG. 18;

FIG. 21 shows in a sectional view a receiving part of the deviceaccording to FIG. 18;

FIG. 22 shows a sectional view of the bone stabilization deviceaccording to the second embodiment.

DETAILED DESCRIPTION

FIG. 1 shows a lower part of the spine anatomy in conjunction withvariously positioned bone anchoring devices 14 a-14 f. The boneanchoring devices each include a bone screw and a receiving part forreceiving and fixing, e.g., a head section of the bone screw. Each ofthe bone anchoring devices 14 a-14 f is anchored in one vertebrae ofeither the thoracic or lumbar spine.

As is apparent from FIG. 1, the interpedicular distance between twoadjacent bone anchoring devices 14 a and 14 b in the high thoracic partdecreases from 25 mm-30 mm towards values of 10-15 mm for respectivebone anchoring devices 14 e and 14 f in the lower lumbar part (whichstabilize L5-S1). As noted above, a rod element 16 designed to furnishthe stabilization by connecting adjacent ones of the anchoring devices14 a-14 f, and which is provided with flexibility and bendingcharacteristics, must preserve a minimum length for a respectiveflexible section.

Hence, when considering the lower lumbar part, a flexible sectionrequiring a length of, e.g., 15 mm cannot easily be positioned betweenrespective receiving parts of conventional bone anchoring devices. Ithas to be noted that a typical receiving part may also contributefurther 6-12 mm to the amount of needed distance.

FIGS. 2 and 3 show an embodiment of a bone anchoring device 14 asproposed herein. FIG. 2 shows an exploded view of the parts involved ina disassembled state, while FIG. 3 shows the device in an assembledstate. First, the basic parts of the device which are partly known inthe art will be described.

The bone anchoring device 14 includes a bone screw 2, a receiving part4, a pressure element 6 and a fixation element 8. The bone screw 2 has athread section 22 for insertion into the bone e.g., a vertebral body(not shown), and a head section 24. In this embodiment, the bone screw 2has a spherically shaped head section 24, but the bone anchoring deviceshall not be limited to the specific shape and function of the headsection 24 and/or the thread section 22. The materials selected for thecomponents may be any biocompatible material or metals such as Titaniumor Titanium alloy.

The receiving part 4 is of substantially symmetric form and has a firstend 40 and a second end 41, which has a tapered profile. From the firstend 40, there extends a first bore 42 to define an inner space of thereceiving part 4, which also is of substantially cylindrical shape. Atan upper portion of an inner wall of the bore 42, an inner thread 45 isformed which may engage with a corresponding outer thread 81 of thefixation element 8 (see also FIGS. 4-8).

The pressure element 6 is positioned within the first bore 42 betweenthe fixation element 8 and the head section 24 of the bone screw 2. Thebone screw 2 is accommodated within a second bore 43 adjacent to thefirst bore 42 and is positioned at the second end 41 opposite to thefirst end 40 of the receiving part 4. The pressure element 6 is providedwith a bottom surface 69 (not shown in detail), which in this specificembodiment is arranged to yield a form-fit connection with thespherically shaped surface of the head section 24 of the bone screw 2(see also FIGS. 9-11).

It may be noted herein that the specific type of connection of the bonescrew 2 as described above refers to a polyaxial bone anchoring device.However, those of ordinary skill in the art will readily recognize thatthe function and effects of the bone anchoring device to be explainedare similarly applicable to monoaxial bone anchoring devices describedbelow with regard to a second embodiment.

Upon screwing-in the fixation element 8 into the thread 45 of thereceiving part 4, pressure is exerted onto the rod element 16 insertedinto receiving part 4. The pressure is then transmitted further to thepressure element 6 in order to lock the bone screw 2 with frictionalforce.

Next, the details of a modification as proposed herein will be describedwith particular reference to FIGS. 4-8, which show enlarged views of thereceiving part 4.

The receiving part 4 is provided with two recesses 44 and 49, whichextend from the first end 40. The recesses define two legs 46 of thereceiving part 4 and are configured to receive the rod element 16 intothe receiving part 4. The first recess 44 has substantially the shape ofa reversed keyhole. The first recess 44 has a bottom section 44 a and anupper section 44 b, wherein the bottom section has a larger width (widthas measured in a direction perpendicular to the axis of the inserted rodelement and perpendicular to the longitudinal axis of the receiving part4), and the upper section has a smaller width. For example, the width ofthe bottom section can be 7.5 mm and the width of the upper section canbe 5.5 mm.

The bottom section 44 a has a substantially circular or oval shape (seeFIG. 8). It has an enlarged width in order to accommodate a steppedportion of the rod element 16. The second recess 49 on the back side inFIGS. 4 and 8, or on the right side in FIG. 6 is of the conventionaltype having a U-shape. Its width in its upper section as well as in itsbottom section can be the same as the upper section 44 b. For example,the width can be 5.5 mm.

An edge 47 defined by an intersection of the an inner wall of the bottomsection 44 a of the first recess 44 with an outer surface of thereceiving part 4 is chamfered in order to facilitate insertion of astepped portion of the rod element 16 upon assembly as will be explainedbelow.

Next, details of the pressure element 6 modified as proposed herein areexplained with reference to FIGS. 9-11. The pressure element 6 has twoleg portions 62, separated by a cylindrical recess 61, and an annularbase portion 65. The pressure element further has a substantiallycylindrical outer surface 63. The cylindrical recess 61 is designed toreceive the rigid section 161 of the rod element 16 and therefore has acorresponding width (e.g., 5 mm) in order to fit the same. Thecylindrical recess has a longitudinal axis which upon insertion of thepressure element in the first bore 42 of the receiving part 4 isoriented perpendicular to the longitudinal axis of that bore 42.

The pressure element 6 further has a stop face 64, which is arranged asa plane surface recessed from the generally cylindrical outer surface63. The stop face 64 is arranged to abut on the end face 163 of thestepped portion 162 of the rod element 16, or vice versa. The stop face64 is accordingly shaped as an annular segment, which becomes apparentfrom the front view of FIG. 10. Preferably, the end face of the steppedportion is also represented by a plane surface perpendicular to thelongitudinal axis of the rod, or of the cylindrical recess respectively.

It may be noted that the fixation element 8 in this embodiment has atits bottom end an extension 82. The extension 82 has a decreaseddiameter smaller than the threaded section. This decreased diameterallows the stepped portion 162 to be accommodated in the inner space ofthe first bore 42 of the receiving part 4. The length of the extension82 along the longitudinal direction of the bore 42 is equal to or largerthan the height of the step due to the stepped portion 162 of the rodelement 16.

A bottom face of this extension 82 exerts pressure onto the rigidsection 161 of the rod element 16, while an angular bottom face (notshown) of the threaded portion of the fixation element 8 may, forexample, exert a pressure onto legs 62 of the pressure element 6.

FIG. 12 shows a cross-sectional view of a bone stabilization device 1including two of the bone anchoring devices 14 as detailed above and astepped rod element 16. FIG. 13 shows an enlarged detail of FIG. 12. Thestepped portion 162 in this embodiment represents a flexible section ofthe rod element 16 comprising for example a helically opened pipeenclosing a bore in which a core being slidable at least at one endthereof is disposed with properties similar to the rod element in EP1757243.

The stepped portion extends through respective first recesses 44 (due tothe bottom section 44 a) and into the internal spaces (due to the stopface 64) of the receiving parts 4 of the corresponding bone anchoringdevices 14, for example devices 14 e and 14 f in FIG. 1. Portions 100,101 of length as schematically indicated in FIG. 12 may thus be saved toaccommodate the stepped portion between the receiving parts 4. Forexample, the lengths 100, 101 can be each 2-4 mm. The minimum length toaccommodate the stepped portion is thus reduced to, for example, 9-11mm, which may comply with the requirements applicable with regard to theL5-S1 stabilization (see FIG. 1).

FIGS. 14-17 illustrate the assembly process of the bone stabilizationdevice 1. FIGS. 14, 15 show side views, while FIGS. 16 and 17 showperspective views of respective steps. First, the bone screws 2 areinserted into the receiving parts 4 through the first and second bores42, 43 followed by anchoring the screws 2 in the respective bones. Then,the rigid sections 161 of the stepped rod element 16 are inserted intorecesses 44, 49. The fixation elements 8 are then screwed in but are notyet fastened (FIGS. 14, 16).

Next, the two receiving parts 4 are shifted towards each other toshorten the mutual distance (indicated by arrows in FIG. 14). Thestepped portion 162 thereby enters into each of the bottom sections 44 aof the recesses 44 wherein the chamfered edges 47 of the recesses 4 helpcompensate for slight misalignments.

Finally, the end faces 163 of the stepped portions 162 abut on the stopfaces 64 of the pressure elements 6 (FIGS. 15, 17).

Another embodiment is illustrated with respect to FIGS. 18-22. Thisembodiment relates to a monoaxial bone anchoring device 214. As comparedwith the first embodiment, similar components are denoted with the samereference numerals. In the following section only different features ofthe second embodiment are described.

In this embodiment, the bone screw part 202 is integrally formed withthe receiving part 204. Thus the thread section 22 extends from thebottom end 41 of the receiving part in a fixed direction (i.e., notrotatable prior to fixation). Hence, contrary to the first embodiment,there is neither a pressure element nor second bore present in thisanchoring device. Instead, the first bore 42 of the receiving part has abottom end, at which is formed a cylindrical recess 261, which issimilarly adapted to receive the rigid section 161 of the rod element16.

Similar to the first embodiment, a plane stop face 264 is orientedtowards a section 44 a of the reverse key-shaped recess 44, which hasthe larger width to receive the stepped portion 162 of the rod element16. The plane of the stop face 264 extends perpendicular to thelongitudinal axis of the cylindrical recess 261, and also similar tostop face 164 according the first embodiment, intersects the inner spaceof the first bore.

It will become apparent to the person skilled in the art, that themodifications proposed herein may be embodied with various otherconfigurations while yielding similar effects without departing from thescope as set forth in the appended claims.

What is claimed is:
 1. A bone anchoring device, comprising: a receivingpart for receiving a rod-shaped implant, the receiving part having afirst end, a second end, a sidewall extending between the first end andthe second end, a first bore extending coaxially with a longitudinalaxis of the receiving part from the first end, and first and secondrecesses each extending into the sidewall from the first end, the firstand second recesses being positioned and configured for insertion of arod-shaped implant through the receiving part; a bone screw having athreaded section for insertion into a bone; and a fixation elementconfigured to fix a rod-shaped implant in the first and second recesses;wherein when the receiving part and the fixation element are assembledtogether, the first recess of the receiving part has a shape of aninverted keyhole, with a bottom section having a second width and anupper section oriented towards the first end of the receiving parthaving a first width smaller than the second width, and wherein agreatest width of the second recess of the receiving part is less thanthe second width.
 2. The bone anchoring device of claim 1, furthercomprising the rod-shaped implant comprising a rigid first sectionhaving substantially the first width, and a stepped portion having agreater thickness than the first width, such that the first recess ofthe receiving part is configured to accommodate the stepped portion ofthe rod-shaped implant.
 3. The bone anchoring device of claim 1, whereinthe bone screw is fixedly attached to the receiving part.
 4. The boneanchoring device of claim 1, wherein the bone screw is pivotablyconnected to the receiving part.
 5. The bone anchoring device of claim4, further comprising a pressure element configured to be inserted inthe receiving part and to be arranged between a head of the bone screwand the fixation element for transmitting pressure to the head of thebone screw.
 6. The bone anchoring device of claim 5, wherein thepressure element has a cylindrical recess defining two legs and adaptedto receive a rod-shaped implant.
 7. The bone anchoring device of claim5, wherein the pressure element comprises a surface having asubstantially cylindrical shape adapted to fit with an inner wall of thefirst bore of the receiving part.
 8. The bone anchoring device of claim1, wherein at least a bottom portion of the first recess of thereceiving part has an edge that is chamfered.
 9. The bone anchoringdevice of claim 1, wherein the second recess of the receiving part has ashape that is different from the shape of the first recess of thereceiving part.
 10. A method of attaching a rod-shaped implant to a bonevia a bone anchoring device, the bone anchoring device comprising a bonescrew having a threaded section for insertion into a bone, a receivingpart having a first end, a second end, a sidewall extending between thefirst end and the second end, a first bore extending coaxially with alongitudinal axis of the receiving part from the first end, and firstand second recesses each extending into the sidewall from the first end,the first and second recesses being positioned and configured forinsertion of the rod-shaped implant through the receiving part, and afixation element configured to fix the rod-shaped implant in the firstand second recesses, the rod-shaped implant comprising a rigid firstsection having a first width, and a stepped portion having a greaterthickness than the first width, the method comprising: attaching thebone anchoring element to a bone; inserting the rod-shaped implant intothe first and second recesses of the receiving part; and assembling thefixation element to the receiving part to fix the rod-shaped implant,wherein when the receiving part and the fixation element are assembledtogether, the first recess of the receiving part has a shape of aninverted keyhole, with a bottom section having a second width greaterthan the first width to accommodate the stepped portion of therod-shaped implant, and an upper section oriented towards the first endof the receiving part having the first width, and wherein a greatestwidth of the second recess of the receiving part is less than the secondwidth to accommodate the rigid first section of the rod-shaped implant.11. A bone anchoring device, comprising: a rod-shaped implant having afirst end, a second end, and a longitudinal axis extending between thefirst end and the second end, wherein a first width of the rod-shapedimplant is a maximum width of the rod-shaped implant measured in adirection perpendicular to the longitudinal axis, and wherein therod-shaped implant has a portion with a second width that is less thanthe first width; and a receiving part for receiving the rod-shapedimplant, the receiving part having a first end, a second end, a centralaxis extending between the first end and the second end, an outersurface, and a recess extending from the first end toward the second endand being configured for insertion of the rod-shaped implant through thereceiving part; wherein the recess of the receiving part forms a shapeof an inverted keyhole in the outer surface of the receiving part,wherein a bottom section of the inverted keyhole has a first widthmeasured in a direction perpendicular to the central axis of thereceiving part, and an upper section of the inverted keyhole openstowards the first end of the receiving part and has a second width thatis smaller than the first width of the receiving part; and wherein thefirst width of the recess of the receiving part is at least the firstwidth of the rod-shaped implant, and wherein the second width of therecess of the receiving part is at least the second width of therod-shaped implant and less than the first width of the rod-shapedimplant.
 12. The bone anchoring device of claim 11, wherein a portion ofthe rod-shaped implant having the first width comprises a flexiblesection.
 13. The bone anchoring device of claim 11, wherein when therod-shaped implant is inserted through the receiving part, a portion ofthe rod-shaped implant having the first width is insertable past theouter surface and into the recess of the receiving part.
 14. The boneanchoring device of claim 13, wherein the portion of the rod-shapedimplant having the first width and that is insertable past the outersurface and into the recess of the receiving part is positioned closestto the first end of the receiving part.